Embodiments of the invention relate generally to medical or non-medical imaging and, more particularly, to a system and method for iterative resolution recovery in diagnostic imaging such as, x-ray, MR, and CT imaging.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
Spatial resolution affects image clarity and diagnostic quality of a CT image. High spatial resolution CT images are generally desired; however, spatial resolution may be degraded in a CT image due to any of multiple sources of resolution degradation. For example, when designing a reconstruction kernel, the balance between spatial resolution and noise is typically addressed. In general, a higher spatial resolution kernel leads to higher noise in the reconstructed image, and the tradeoff between the two is not linear. That is, the increase in noise is much faster than an increase in the spatial resolution. As a result, the spatial resolution of a CT study generally has to be artificially lowered in order to make sure the object-of-interest is not masked out by the noise in the image. The artificial lowering of spatial resolution often leads to undesirable features such as blooming in a reconstructed image from certain objects (e.g., calcified plaque or stent) or bright areas of the image. Such blooming may inflate measurements of a particular tissue, causing the object to appear larger in size than it really is.
Therefore, it would be desirable to design a system and method that reduces blooming artifacts in reconstructed images without significant increase in image noise.